[constexpr.functions]

# 16 Library introduction [[library]](./#library)

## 16.4 Library-wide requirements [[requirements]](requirements#constexpr.functions)

### 16.4.6 Conforming implementations [[conforming]](conforming#constexpr.functions)

#### 16.4.6.7 Constexpr functions and constructors [constexpr.functions]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L3732)

This document explicitly requires that certain standard library functions areconstexpr ([[dcl.constexpr]](dcl.constexpr "9.2.6 The constexpr and consteval specifiers"))[.](#1.sentence-1)

An implementation shall not declare
any standard library function signature as constexpr except for those where
it is explicitly required[.](#1.sentence-2)

Within any header that provides any non-defining declarations of constexpr
functions or constructors an implementation shall provide corresponding definitions[.](#1.sentence-3)